JP5109161B2 - Method for producing perfluoropolymer, production apparatus, and method for producing electrolyte membrane for polymer electrolyte fuel cell - Google Patents

Description

  The present invention relates to a method for producing a perfluoropolymer, a production apparatus, and a method for producing an electrolyte membrane for a polymer electrolyte fuel cell.

Perfluoropolymers are used in various fields such as coatings for chemical plants, semiconductor manufacturing equipment, etc .; coatings for electric wires, optical fibers, etc .; automobile parts. Recently, perfluoropolymers having —SO ₃ H groups have attracted attention as materials for electrolyte membranes for polymer electrolyte fuel cells.

However, the perfluoropolymer is not completely perfluorinated immediately after being obtained by polymerizing a perfluoromonomer such as perfluorocarbon, and a —COOH group, —CF═CF _{2 is} attached to a part of the molecular chain end. Group, a —COF group, a —CF ₂ H group and other unstable functional groups (hereinafter referred to as unstable terminal groups). For this reason, when used as a fuel cell electrolyte for a long time, there is a problem that the perfluoropolymer gradually decomposes due to the presence of unstable end groups, resulting in a decrease in generated voltage. Further, as the perfluoropolymer is decomposed, the mechanical strength of the electrolyte membrane is lowered, causing pinholes, cracks, peeling, and the like, which makes it impossible to use the fuel cell.

The following method has been proposed as a method for producing a perfluoropolymer with reduced unstable end groups.
A sheet of 2 mm thickness made of a copolymer of tetrafluoroethylene and CF ₂ ═CFOCF ₂ CF (CF ₃ ) O (CF ₂ ) ₂ SO ₂ F is placed in a pressure resistant reactor and fluorinated at 190 ° C. for 4 hours. A method of performing processing (Patent Document 1).

However, this method has the following problems.
(I) It takes several hours to raise the temperature of the pressure resistant reactor and several hours to lower it.
(Ii) Since the sheet is thick, it takes several hours to fluorinate to the center.
(Iii) Even if the thickness of the sheet is reduced in order to shorten the time of the fluorination treatment, the amount of perfluoropolymer that can be produced by one treatment is reduced.
(Iv) In order to remove the perfluoropolymer from the pressure resistant reactor, it is necessary to completely extract the fluorine gas, but it takes a long time to extract the fluorine gas from the pressure resistant reactor and replace the inside of the pressure resistant reactor with nitrogen gas. It takes about a day.
(V) Because of the batch type, continuous fluorination treatment cannot be performed.

From the problems (i) to (v), the method described in Patent Document 1 has a problem that a perfluoropolymer with reduced unstable terminal groups cannot be efficiently produced.
International Publication No. 2004/102714 Pamphlet (Example 1 on page 9)

  The present invention provides a production method capable of efficiently producing a perfluoropolymer with reduced unstable end groups, a production apparatus, and a production method capable of efficiently producing an electrolyte membrane for a polymer electrolyte fuel cell excellent in durability. The purpose is to do.

The method for producing a perfluoropolymer of the present invention includes a treatment in which a polymer obtained by polymerizing a perfluoromonomer is extruded to form a strand, and a gas containing 3 to 50% by volume of fluorine gas is brought into contact with the strand. It is characterized by that.
In the method for producing a perfluoropolymer of the present invention, it is preferable that a gas containing fluorine gas is brought into contact with the strand at 150 to 350 ° C.

The polymer preferably has a —SO ₂ F group.
The polymer is preferably a copolymer of tetrafluoroethylene and a compound represented by the following formula (1).
CF ₂ = CF (OCF ₂ CFX) _p (O) _q (CF ₂ ) _n SO ₂ F (1)
However, X is a fluorine atom or a trifluoromethyl group, p is an integer of 0 to 8, q is 0 or 1, n is an integer of 0 to 8, and p + n> 0.

In the method for producing perfluoropolymer of the present invention, a polymer obtained by polymerizing perfluoromonomer is melted and extruded by a melting / extrusion means, and a plurality of holes are formed in the extruded molten polymer. It is preferable to make it a strand through a die.
The perfluoropolymer production apparatus of the present invention has a plurality of pores formed by melting and extruding means for melting and extruding a polymer obtained by polymerizing perfluoromonomer, and using the extruded molten polymer as a strand. And a fluorination tank in which a gas containing 3 to 50% by volume of fluorine gas is brought into contact with the strand.

The method for producing an electrolyte membrane for a polymer electrolyte fuel cell of the present invention is obtained by obtaining a perfluoropolymer having —SO ₂ F groups by the method for producing a perfluoropolymer of the present invention, and then molding the perfluoropolymer. The film is characterized by being subjected to hydrolysis treatment and acidification treatment.
The method for producing an electrolyte membrane for a polymer electrolyte fuel cell of the present invention is obtained by obtaining a perfluoropolymer having —SO ₂ F group by the method for producing a perfluoropolymer of the present invention, and then hydrolyzing the perfluoropolymer. And an acid-forming treatment, and the treated perfluoropolymer is formed into a film.

According to the method for producing a perfluoropolymer of the present invention, a perfluoropolymer with reduced unstable end groups can be produced efficiently.
According to the perfluoropolymer production apparatus of the present invention, it is possible to efficiently produce a perfluoropolymer with reduced unstable terminal groups.
According to the method for producing an electrolyte membrane for a polymer electrolyte fuel cell of the present invention, an electrolyte membrane for a polymer electrolyte fuel cell excellent in durability can be efficiently produced.

  In the present specification, a compound represented by the formula (1) is referred to as a compound (1). The same applies to compounds represented by other formulas.

[Example 1]
(Perfluoropolymer production equipment)
FIG. 1 is a schematic configuration diagram showing an example of an apparatus for producing a perfluoropolymer of the present invention. The perfluoropolymer manufacturing apparatus 10 includes a melting / extrusion means 11, a die 12 attached to the tip of the melting / extrusion means 11 and having a plurality of holes, and the die 12 attached to the head. And a fluorination tank 13.

  Examples of the melting / extrusion means 11 include a single-screw extruder, a twin-screw extruder, a conical feeder, a gear pump, and the like. A single-screw extruder is preferable in that the molten polymer can be stably extruded. FIG. 1 is an example of a single screw extruder.

The hole diameter of the die 12 is preferably 0.5 to 5 mm, particularly preferably 1 to 3 mm. By setting the hole diameter to 0.5 mm or more, the strand is difficult to break. By setting the pore diameter to 5 mm or less, the strand does not become too thick, the diffusion distance of the fluorine gas becomes sufficiently short, and the unstable end group can be sufficiently fluorinated.
The larger the number of holes in the die 12, the more efficiently the perfluoropolymer can be produced. Even with the same processing amount, it is possible to process efficiently by increasing the number of strands and reducing the diameter of the strands instead of increasing the hole diameter of the die 12. The number of holes in the die 12 may be appropriately set according to the inner diameter of the fluorination tank 13 or the like.

  The fluorination tank 13 includes a vertical cylindrical pipe 17 having a die 12 attachment port at the head, a gas supply port 14 and a gas exhaust port 15 at the side surface, and a polymer outlet 16 at the bottom, and a periphery of the cylindrical tube 17. And a heater 18 attached to the. The material for the cylindrical tube is preferably nickel. In FIG. 1, the gas supply port 14 is disposed at the upper part of the fluorination tank 13 and the gas exhaust port 15 is disposed at the lower part. However, these positions may be reversed. That is, the gas supply port 14 may be disposed in the lower part of the fluorination tank 13 and the gas exhaust port 15 may be disposed in the upper part.

(Method for producing perfluoropolymer)
Perfluoropolymer production using the perfluoropolymer production apparatus 10 is performed as follows.
(I) A polymer is obtained by polymerizing one or more perfluoromonomers.
(Ii) The obtained polymer is melted by the melting / extrusion means 11 and extruded to the die 12.
(Iii) The extruded molten polymer is passed through a die 12 to form a strand 1.
(Iv) While the strand 1 is lowered in the fluorination tank 13, the strand 1 is brought into contact with a gas containing fluorine gas.
(V) The perfluoropolymer 2 accumulated at the bottom of the fluorination tank 13 is taken out from the polymer outlet 16.
The steps (ii) to (v) are, as shown in FIG. 1, a perfluoropolymer production apparatus in which a melting / extrusion means 11, a die 12 and a fluorination tank 13 for performing each step are integrally provided. 10 is performed continuously.

Examples of the perfluoromonomer include a perfluorovinyl compound having a —SO ₂ F group, a perfluoroolefin, and perfluoro (alkyl vinyl ether).

Examples of the perfluorovinyl compound having a —SO ₂ F group include the compound (1).
CF ₂ = CF (OCF ₂ CFX) _p (O) _q (CF ₂ ) _n SO ₂ F (1)
However, X is a fluorine atom or a trifluoromethyl group, p is an integer of 0 to 8, q is 0 or 1, n is an integer of 0 to 8, and p + n> 0.

Examples of compound (1) include compounds (1-1) to (1-4).
CF ₂ = CFO (CF ₂ ) _r SO ₂ F (1-1)
CF ₂ = CFOCF ₂ CF (CF ₃ ) O (CF ₂ ) _s SO ₂ F (1-2)
CF ₂ = CF (CF ₂ ) _t SO ₂ F (1-3)
_{CF 2 = CF [OCF 2 CF} (CF 3)] z O (CF 2) 2 SO 2 F ··· (1-4)
However, r is an integer of 1-9, s is an integer of 1-8, t is an integer of 0-8, z is 2 or 3.

  Examples of the perfluoroolefin include tetrafluoroethylene and hexafluoropropylene.

Examples of perfluoro (alkyl vinyl ether) include compound (2).
CF ₂ = CF (OCF ₂ CFY) _y OR ^f (2)
However, Y is a fluorine atom or a trifluoromethyl group, y is an integer of 0 to 3, and ^Rf is a perfluoroalkyl group.

Examples of compound (2) include compounds (2-1) to (2-3).
CF ₂ = CFO (CF ₂ ) _v CF ₃ (2-1)
CF ₂ = CFOCF ₂ CF (CF ₃ ) O (CF ₂ ) _w CF ₃ (2-2)
_{CF 2 = CF [OCF 2 CF} (CF 3)] x O (CF 2) 2 CF 3 ··· (2-3)
However, v is an integer of 1-8, w is an integer of 1-8, and x is an integer of 1-3.

As a polymer obtained by polymerizing perfluoromonomer (hereinafter referred to as polymer), a copolymer of tetrafluoroethylene and perfluoro (alkyl vinyl ether) (hereinafter referred to as PFA), tetrafluoro Examples thereof include a copolymer of ethylene and hexafluoropropylene (hereinafter referred to as FEP), a polymer having a —SO ₂ F group, and the like. As a raw material for the electrolyte membrane for a polymer electrolyte fuel cell, a polymer having a —SO ₂ F group is preferable, and a copolymer of tetrafluoroethylene and compound (1) (hereinafter referred to as copolymer (A)). .) Is particularly preferred.

The melting temperature of the polymer (the temperature in the melting / extrusion means 11) is preferably 180 to 240 ° C in the case of the copolymer (A), preferably 330 to 380 ° C in the case of PFA, and 310 to 300 in the case of FEP. 360 ° C is preferred.
The extrusion rate (g / min) of the polymer is such that the contact time between the strand and the gas containing the fluorine gas and the strand diameter are described later according to the number of holes in the die 12, the hole diameter, and the length of the fluorination tank 13. What is necessary is just to set suitably so that it may become a range.

In order to increase the efficiency of fluorination, it is preferable to appropriately adjust the melt viscosity of the polymer at the temperature passing through the die 12. For example, in the case of the copolymer (A), the melt viscosity is preferably 1000 to 7000 Pa · sec. If the melt viscosity is too high, it may be difficult to extrude the polymer. If the melt viscosity is too low, the strands drop quickly, and the contact time with a gas containing fluorine gas is shortened, and the fluorination of unstable terminal groups may be insufficient.
The polymer TQ is preferably 150 ° C. or higher, more preferably 200 ° C. or higher. The TQ of the polymer is preferably 350 ° C. or less, and more preferably 300 ° C. or less.
The TQ value (unit: ° C.) is an index of the molecular weight of the polymer. The extrusion amount when the polymer is melt-extruded under the condition of the extrusion pressure of 2.94 MPa using a nozzle having a length of 1 mm and an inner diameter of 1 mm. The temperature is 100 mm ³ / sec.

The temperature (temperature in the fluorination tank) when contacting the strand with a gas containing fluorine gas is preferably 150 to 350 ° C.
Specifically, in the case of a copolymer (A), 150-200 degreeC is more preferable, and 170-190 degreeC is especially preferable. By setting the temperature to 150 ° C. or higher, unstable terminal groups can be sufficiently fluorinated. By setting the temperature to 200 ° C. or lower, decomposition of the —SO ₂ F group can be suppressed.
In the case of PFA, 300 to 350 ° C. is more preferable, and in the case of FEP, 230 to 300 ° C. is more preferable.

The fluorine gas is diluted with an inert gas such as nitrogen gas and supplied as a mixed gas from the gas supply port 14. The fluorine gas concentration in the mixed gas is 3 to 50% by volume. If the fluorine gas concentration is too low, the efficiency of the reaction may be lowered, and it becomes necessary to increase the time for the strand and the polymer to come into contact with each other, which is not preferable in terms of production efficiency. More preferably, it is 5 volume% or more. Further, if the fluorine gas concentration is too high, there is a risk of causing decomposition of the polymer, and it is not preferable in terms of cost because it is necessary to install equipment for performing it safely. More preferably, it is 25 volume% or less.
The pressure in the fluorination tank 13 is preferably 1 MPa (gauge pressure) or less, and more preferably 0 to 0.5 MPa. The pressure in the fluorination tank 13 is kept constant by adjusting the exhaust amount from the gas exhaust port 15.
The fluorine gas is absorbed into the polymer strand and diffuses to react with unstable end groups. An inert gas such as nitrogen gas used as a diluent gas also dissolves in the polymer, but does not inhibit the reaction. In addition, the inert gas exists as bubbles in the strand, and the efficiency of degassing does not decrease. On the other hand, for example, when a gas is brought into contact with a polymer in an extruder, or when a gas is brought into contact with a polymer while applying force to the polymer, bubbles are finely dispersed and degassing treatment takes time.

  The strand diameter is preferably 0.1 to 1 mm, more preferably 0.1 to 0.3 mm, at the narrowest part (near the bottom of the fluorination tank). When the strand diameter is 0.1 mm or more, the strand is difficult to break. By setting the strand diameter to 1 mm or less, unstable terminal groups can be sufficiently fluorinated.

  The contact time between the strand and the gas containing fluorine gas is preferably 5 to 30 minutes. By setting the contact time to 5 minutes or longer, the unstable terminal group can be sufficiently fluorinated. There is no problem even if the contact time exceeds 30 minutes, but 30 minutes or less is preferable from the viewpoint of processing efficiency. The contact time is obtained by dividing the throughput (ml / min) by the total area of the die holes to obtain the linear velocity (m / sec) of the die, and the descending distance (height of the fluorination tank 12) by the linear velocity. It is calculated by dividing.

[Example 2]
(Perfluoropolymer production equipment)
FIG. 2 is a schematic configuration diagram illustrating another example of the perfluoropolymer production apparatus of the present invention. The perfluoropolymer manufacturing apparatus 20 includes a melting / extrusion means 11, a die 12 attached to the tip of the melting / extrusion means 11 and having a plurality of holes, and the die 12 attached to the head. A fluorination tank 13, a take-out pipe 21 connected to a polymer take-out port of the fluorination tank 13, and a pump 22 provided in the middle of the take-out pipe 21 are provided.

As the melting / extrusion means 11, the die 12, and the fluorination tank 13, the same ones as those in the first embodiment are used.
The take-out pipe 21 is filled with perfluoropolymer 2 and sealed with perfluoropolymer 2 so that the fluorine gas in the fluorination tank 13 does not leak outside through the take-out pipe 21 (material seal). It is in a state that has been.
Examples of the pump 22 include a gear pump and a single screw extruder.

(Method for producing perfluoropolymer)
The production of perfluoropolymer using the perfluoropolymer production apparatus 20 is performed as follows.
(I) to (iv) are performed in the same manner as in the first embodiment.
(V) In a state where the take-out pipe 21 is sufficiently material-sealed with the perfluoropolymer 2, the operation of the pump 22 is started, and the perfluoropolymer 2 is taken out from the take-out pipe 21 continuously.
In steps (ii) to (v), as shown in FIG. 2, the melting / extrusion means 11, the die 12, the fluorination tank 13, the take-out pipe 21 and the pump 22 for performing each step are integrally provided. The perfluoropolymer production apparatus 20 continuously performs the process.

[Example 3]
(Perfluoropolymer production equipment)
FIG. 3 is a schematic configuration diagram showing another example of the perfluoropolymer production apparatus of the present invention. The perfluoropolymer production apparatus 30 includes a melting / extrusion means 11, a die 12 attached to the tip of the melting / extrusion means 11 and having a plurality of holes, and the die 12 attached to the head. A fluorination tank 13, a deaeration tank 31, and a take-out pipe 32 having one end located in the fluorination tank 13 and the other end connected to the deaeration tank 31 are provided.

As the melting / extrusion means 11, the die 12, and the fluorination tank 13, the same ones as those in the first embodiment are used.
The deaeration tank 31 has a die 33 having a plurality of holes formed in the head, a deaeration port 34 on the side surface, and a polymer outlet 35 on the bottom.
The take-out pipe 32 is a pipe having a polymer receiver 36 formed at one end, and sealed with perfluoropolymer so that the fluorine gas in the fluorination tank 13 does not leak into the deaeration tank 31 through the take-out pipe 32 ( The material is sealed.

(Method for producing perfluoropolymer)
Perfluoropolymer production using the perfluoropolymer production apparatus 30 is performed as follows.
(I) to (iv) are performed in the same manner as in the first embodiment.
(V) The gas in the deaeration tank 31 is degassed from the deaeration port 34 in a state where the take-out pipe 32 is sufficiently material-sealed with perfluoropolymer. The perfluoropolymer is introduced into the degassing tank 31 by the differential pressure between the fluorination tank 13 and the degassing tank 31.
(Vi) The perfluoropolymer is passed through the die 33 to form a strand 3.
(Vii) While lowering the strand 3 in the degassing tank 31, the fluorine gas remaining in the strand 3 is degassed.
(Viii) The perfluoropolymer 4 accumulated at the bottom of the deaeration tank 31 is taken out from the polymer outlet 35.
As shown in FIG. 3, the steps (ii) to (viii) are performed by integrating the melting / extrusion means 11, the die 12, the fluorination tank 13, the take-out pipe 32, and the deaeration tank 31 that perform each process. The continuous perfluoropolymer production apparatus 30 is used.

The pressure in the deaeration tank 31 is preferably 0.1 to 0.6 MPa (gauge pressure) lower than the pressure in the fluorination tank 13.
When the perfluoropolymer has a high viscosity and cannot be introduced into the deaeration tank 31 due to the differential pressure, a pump may be provided in the take-out pipe 32.

[Example 4]
(Perfluoropolymer production equipment)
FIG. 4 is a schematic configuration diagram showing another example of the perfluoropolymer production apparatus of the present invention. The perfluoropolymer manufacturing apparatus 40 includes a melting / extrusion means 11, a die 12 attached to the tip of the melting / extrusion means 11 and having a plurality of holes, and the die 12 attached to the head. A fluorination tank 13, a twin screw extruder 41, a discharge pipe 42 having one end connected to the polymer outlet of the fluorination tank 13 and the other end connected to a polymer supply port of the twin screw extruder 41, A die 43 attached to the tip of the extruder 41 and a pelletizer 44 are provided.

As the melting / extrusion means 11, the die 12, and the fluorination tank 13, the same ones as those in the first embodiment are used.
The twin-screw extruder 41 has a vent port 45 and performs degassing of the perfluoropolymer 2.
The take-out pipe 42 is in a state (material seal) sealed with the perfluoropolymer 2 so that the fluorine gas in the fluorination tank 13 does not leak into the twin-screw extruder 41 through the take-out pipe 42.
The die 43 turns the perfluoropolymer 2 extruded from the twin screw extruder 41 into a strand 5.
The pelletizer 44 cuts the strands 5 to produce perfluoropolymer pellets.

(Method for producing perfluoropolymer)
The production of perfluoropolymer using the perfluoropolymer production apparatus 40 is performed as follows.
(I) to (iv) are performed in the same manner as in the first embodiment.
(V) In a state where the take-out pipe 42 is sufficiently material-sealed with the perfluoropolymer 2, the operation of the twin screw extruder 41 is started, and the perfluoropolymer 2 is introduced into the twin screw extruder 41.
(Vi) While the perfluoropolymer 2 is melted by the twin-screw extruder 41, the fluorine gas remaining in the perfluoropolymer 2 is degassed.
(Vii) The perfluoropolymer 2 extruded from the twin-screw extruder 41 is passed through a die 43 to form a strand 5.
(Viii) The strand 5 is cut by the pelletizer 44 to obtain perfluoropolymer pellets.
As shown in FIG. 3, the steps (ii) to (viii) include a melting / extrusion means 11, a die 12, a fluorination tank 13, a take-out pipe 42, a twin screw extruder 41, and a pelletizer 44 that perform each step. It is carried out continuously by the perfluoropolymer production apparatus 40 provided in series.

  The melting temperature of the perfluoropolymer 2 (the temperature of the twin-screw extruder 41) may be approximately the same as the melting temperature of the polymer in the melting / extrusion means 11.

[Use]
The perfluoropolymer obtained by the method for producing a perfluoropolymer of the present invention is used in coatings for chemical plants, semiconductor manufacturing apparatuses, etc .; coatings for electric wires, optical fibers, etc .;
In particular, a perfluoropolymer obtained by converting a —SO ₂ F group into a —SO ₃ H group by subjecting a perfluoropolymer having —SO ₂ F groups to hydrolysis and acidification treatment is a solid polymer fuel. It is useful as an electrolyte polymer included in an electrolyte polymer constituting an electrolyte membrane for a battery, and an anode and a cathode for the fuel cell.
Hereinafter, a method for producing an electrolyte membrane for a polymer electrolyte fuel cell will be described.

The electrolyte membrane for a polymer electrolyte fuel cell is obtained by molding (i) a perfluoropolymer having a —SO ₂ F group obtained by the perfluoropolymer production method of the present invention into a membrane, and hydrolyzing the membrane. Hydrolysis treatment and acidification treatment are performed on the perfluoropolymer having a —SO ₂ F group obtained by the method of performing the treatment and the acidification treatment, or (ii) the perfluoropolymer production method of the present invention, It is manufactured by a method in which a perfluoropolymer after treatment is formed into a film.

  Examples of the method for forming a perfluoropolymer into a film include an extrusion molding method and a casting method.

The hydrolysis treatment is performed, for example, by bringing a perfluoropolymer having a —SO ₂ F group or a membrane thereof into contact with an alkaline aqueous solution. Examples of the alkaline aqueous solution include a potassium hydroxide aqueous solution and a sodium hydroxide aqueous solution. The alkaline aqueous solution may contain an alcohol such as methanol.

  The acidification treatment is performed, for example, by bringing a hydrolyzed perfluoropolymer or a film thereof into contact with an acidic liquid. Examples of the acidic liquid include sulfuric acid, nitric acid, hydrochloric acid and the like. After the acidification treatment, the perfluoropolymer or its film is preferably washed with water.

When used as an electrolyte membrane for a polymer electrolyte fuel cell, the concentration of —SO ₃ H groups, that is, the ion exchange capacity is preferably 0.5 to 2.0 meq / g dry resin, and 0.7 to 1.6. A milliequivalent / gram dry resin is particularly preferred. By setting the ion exchange capacity to 0.5 meq / g dry resin or more, an electrolyte membrane with low resistance is obtained. By setting the ion exchange capacity to 2.0 meq / g dry resin or less, an electrolyte membrane having high mechanical strength is obtained.

The durability of a perfluoropolymer having a —SO ₃ H group or a film thereof can be evaluated by a Fenton reagent immersion test. The test is a test in which a polymer is immersed in a Fenton reagent containing hydrogen peroxide and divalent iron ions, and fluorine ions eluted into the Fenton reagent due to polymer degradation are measured. The conditions of the Fenton reagent immersion test are usually a hydrogen peroxide concentration of 1 to 30% by mass, a divalent iron ion concentration of 10 to 500 ppm, an immersion temperature of 25 to 90 ° C., and an immersion time of 0.5 to 24 hours. Since the perfluoropolymer obtained by the present invention has stable end groups, the amount of ions to be eluted is small. Therefore, when used as an electrolyte membrane for a polymer electrolyte fuel cell, a polymer electrolyte fuel cell having excellent durability can be provided.

  In the method for producing a perfluoropolymer of the present invention described above, a polymer obtained by polymerizing a perfluoromonomer is extruded to form a strand, and a gas containing fluorine gas is brought into contact with the strand. The fluorination treatment can be performed in a shorter time compared to the conventional method in which a gas containing fluorine gas is brought into contact with the sheet. Moreover, since a strand can be supplied continuously, a fluorination process can be performed continuously. As a result, it is possible to efficiently produce a perfluoropolymer with reduced unstable end groups. In addition, if the perfluoropolymer having unstable terminal groups reduced by the fluorination treatment is continuously taken out from the fluorination tank, the perfluoropolymer having reduced unstable terminal groups can be produced more efficiently.

In the method for producing a perfluoropolymer of the present invention, the polymer obtained by polymerizing the perfluoromonomer is extruded to form a strand, and the strand is brought into contact with a gas containing fluorine gas. There is no mechanical sliding part when contacting with a gas containing fluorine gas. That is, it has the effect of suppressing contamination from the reactor material due to mechanical sliding in a corrosive environment.
In the method for producing an electrolyte membrane for a polymer electrolyte fuel cell of the present invention, a perfluoropolymer having a —SO ₂ F group obtained by the method for producing a perfluoropolymer of the present invention is used. Therefore, an electrolyte membrane for a polymer electrolyte fuel cell excellent in durability can be efficiently produced.

EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.
Examples 1, 2, and 5 to 9 are examples, and examples 3 and 4 are comparative examples.
(TQ value)
Using a flow tester CFT-500A (manufactured by Shimadzu Corporation), the extrusion amount of the polymer was measured while changing the temperature, and the TQ value at which the extrusion amount was 100 mm ³ / second was determined.

[Example 1]
A powder of a copolymer (A-1) of tetrafluoroethylene and CF ₂ ═CFOCF ₂ CF (CF ₃ ) O (CF ₂ ) ₂ SO ₂ F was prepared. The ion exchange capacity of the perfluoropolymer having a —SO ₃ H group obtained by subjecting the copolymer (A-1) to the hydrolysis treatment and acidification treatment described later is 1.1 meq / g dry. Resin. The TQ of the copolymer (A-1) was 220 ° C.
As a perfluoropolymer production apparatus, the apparatus shown in FIG. 1 was used.

  The copolymer (A-1) was melted at 230 ° C. with a single-screw extruder (Randcastle, φ12.7 mm) and extruded to a die at an extrusion speed of 2.7 g / min. The temperature of the connecting portion between the single screw extruder and the fluorination tank was 200 ° C. The extruded molten polymer A was passed through three holes (φ3 mm) of the die to form a strand. While the strand was lowered in a 15 L fluorination tank, a gas containing fluorine gas was brought into contact with the strand. The temperature in the fluorination tank was 190 ° C., and the pressure was 0.2 MPa. A mixed gas of 7.5% by volume of fluorine gas and 92.5% by volume of nitrogen gas is continuously supplied to the fluorination tank at 300 ml / min, and the gas in the fluorination tank is supplied to the pressure in the fluorination tank. Was exhausted so that was constant. The strand diameter was 0.3 mm at the lowest end of the strand.

After supplying the copolymer (A-1) to the fluorination tank for 30 minutes, the gas in the fluorination tank was extracted, and the gas in the fluorination tank was replaced with nitrogen gas. After the temperature in the fluorination tank dropped to room temperature, the perfluoropolymer collected at the bottom of the fluorination tank was taken out.
The perfluoropolymer was immersed in an alkaline aqueous solution containing 20% by mass of methanol and 10% by mass of potassium hydroxide to perform a hydrolysis treatment. Next, the perfluoropolymer was washed with sulfuric acid for acidification treatment, and further washed with ion exchange water to obtain a perfluoropolymer having —SO ₃ H groups.

(Fenton reagent immersion test)
The perfluoropolymer having —SO ₃ H groups was kept in a glove box with nitrogen gas flowing for 24 hours, and about 0.1 g was weighed in the glove box. A perfluoropolymer having —SO ₃ H groups was immersed in 50 g of a Fenton reagent containing 3% by mass of hydrogen peroxide and 200 ppm of divalent iron ions at 40 ° C. for 16 hours. After removing the polymer, the mass of the Fenton reagent was measured, the fluorine ion concentration in the Fenton reagent was measured with an ion meter, and the fluorine ion elution amount was calculated. The fluorine ion elution amount was 0.0015%.

[Example 2]
The copolymer (A-1) was fluorinated in the same manner as in Example 1 except that the extrusion speed was changed to 5.6 g / min, to obtain a perfluoropolymer. The strand diameter was φ0.6 mm at the narrowest point.
The obtained perfluoropolymer was subjected to the Fenton reagent immersion test in the same manner as in Example 1. The fluorine ion elution amount was 0.0068% of the total fluorine amount in the immersed polymer.

[Example 3 (comparative example)]
The copolymer (A-1) not subjected to fluorination treatment was subjected to a Fenton reagent immersion test in the same manner as in Example 1. The fluorine ion elution amount was 0.063% of the total fluorine amount in the immersed polymer.

[Example 4 (comparative example)]
A 200 ml nickel reactor was prepared. The reactor (5) was charged with 5 g of the copolymer (A-1), the same mixed gas as in Example 1 was charged to a pressure of 0.25 MPa, held at 180 ° C. for 4 hours, fluorinated, and the perfluoropolymer was Obtained.
The obtained perfluoropolymer was subjected to the Fenton reagent immersion test in the same manner as in Example 1. The fluorine ion elution amount was 0.005% of the total fluorine amount in the immersed polymer.

[Example 5]
Before starting the fluorination treatment, the mixed gas was charged to 0.2 MPa in the fluorination tank, and the fluorine of the copolymer (A-1) was the same as in Example 1 except that the mixed gas was not additionally supplied. To obtain a perfluoropolymer.
The obtained perfluoropolymer was subjected to the Fenton reagent immersion test in the same manner as in Example 1. The fluorine ion elution amount was 0.0006% of the total fluorine amount in the immersed polymer.

[Example 6]
Before starting the fluorination treatment, the mixed gas is charged to 0.1 MPa in the fluorination tank, and the fluorine of the copolymer (A-1) is the same as in Example 1 except that the mixed gas is not additionally supplied. To obtain a perfluoropolymer.
The obtained perfluoropolymer was subjected to the Fenton reagent immersion test in the same manner as in Example 1. The fluorine ion elution amount was 0.0069% of the total fluorine amount in the immersed polymer.

[Example 7]
Before starting the fluorination treatment, the mixed gas is charged to 0.01 MPa in the fluorination tank, and the fluorine of the copolymer (A-1) is the same as in Example 1 except that the mixed gas is not additionally supplied. To obtain a perfluoropolymer.
The obtained perfluoropolymer was subjected to the Fenton reagent immersion test in the same manner as in Example 1. The fluorine ion elution amount was 0.0045% of the total fluorine amount in the immersed polymer.

[Example 8]
As the perfluoropolymer production apparatus, the apparatus shown in FIG. 3 is used to perform the fluorination treatment while continuously taking out the perfluoropolymer accumulated at the bottom of the fluorination tank. The copolymer (A-1) was fluorinated in the same manner as in Example 1 except that the pressure was 3 MPa to obtain a perfluoropolymer.
The obtained perfluoropolymer was subjected to the Fenton reagent immersion test in the same manner as in Example 1. The fluorine ion elution amount was below the measurement limit.

[Example 9]
The perfluoropolymer taken out from the fluorination tank obtained in Example 1 was press-molded to produce a film having a thickness of about 30 μm. The obtained membrane was hydrolyzed and acidified to convert —SO ₂ F groups into —SO ₃ H groups. This film was a good film without cracks.

The perfluoropolymer having a —SO ₂ F group obtained by the method for producing a perfluoropolymer of the present invention has a reduced unstable terminal group and is excellent in durability for an electrolyte membrane for a polymer electrolyte fuel cell It is particularly useful as a raw material.

It is a schematic block diagram which shows an example of the manufacturing apparatus of the perfluoropolymer of this invention. It is a schematic block diagram which shows the other example of the manufacturing apparatus of the perfluoropolymer of this invention. It is a schematic block diagram which shows the other example of the manufacturing apparatus of the perfluoropolymer of this invention. It is a schematic block diagram which shows the other example of the manufacturing apparatus of the perfluoropolymer of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Strand 10 Perfluoropolymer manufacturing apparatus 11 Melting / extrusion means 12 Die 13 Fluorination tank 20 Perfluoropolymer manufacturing apparatus 30 Perfluoropolymer manufacturing apparatus 40 Perfluoropolymer manufacturing apparatus

Claims (8)

  A method for producing a perfluoropolymer, comprising a process of extruding a polymer obtained by polymerizing a perfluoromonomer to form a strand, and contacting the strand with a gas containing 3 to 50% by volume of fluorine gas.   The manufacturing method of the perfluoropolymer of Claim 1 which makes the said gas contact a strand at 150-350 degreeC. Polymer has a -SO ₂ F group, the manufacturing method of the perfluoropolymer according to claim 1 or 2. The method for producing a perfluoropolymer according to claim 3, wherein the polymer is a copolymer of tetrafluoroethylene and a compound represented by the following formula (1).
CF ₂ = CF (OCF ₂ CFX) _p (O) _q (CF ₂ ) _n SO ₂ F (1)
However, X is a fluorine atom or a trifluoromethyl group, p is an integer of 0 to 8, q is 0 or 1, n is an integer of 0 to 8, and p + n> 0.   The polymer obtained by polymerizing the perfluoromonomer is melted and extruded by a melting / extrusion means, and the extruded molten polymer is passed through a die having a plurality of holes to form a strand. 5. A method for producing a perfluoropolymer according to any one of 4 above. Melting / extrusion means for melting and extruding a polymer obtained by polymerizing perfluoromonomer;
A die in which a plurality of holes are formed with the extruded molten polymer as a strand;
A perfluoropolymer production apparatus, comprising: a fluorination tank in which a strand is brought into contact with a gas containing 3 to 50% by volume of fluorine gas. After obtaining a perfluoropolymer by the method for producing a perfluoropolymer according to claim 3 or 4, the perfluoropolymer is molded into a film, and the film is subjected to hydrolysis treatment and acidification treatment. A method for producing an electrolyte membrane for a molecular fuel cell. After obtaining a perfluoropolymer by the method for producing a perfluoropolymer according to claim 3 or 4, the perfluoropolymer is subjected to hydrolysis treatment and acidification treatment, and the treated perfluoropolymer is molded to form a film. A method for producing an electrolyte membrane for a polymer electrolyte fuel cell.

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